1. Field of the Invention
In self-igniting internal combustion engines, besides unit fuel injectors and pump-line-nozzle systems, reservoir-type injection systems are used for injecting fuel. These injection systems include a high-pressure reservoir, which is supplied with fuel at high pressure via a high-pressure pump. The high-pressure pump represents the interface between the high-pressure and low-pressure parts of the injection system. The high-pressure pump includes a pressure regulating valve, which serves on the one hand to open at excessively high pressure in the high-pressure reservoir, so that fuel flows out of the high-pressure reservoir back to the fuel tank via a collection line, and on the other, at excessively low pressure in the high-pressure reservoir, to seal off the high-pressure side from the low-pressure side.
2. Description of the Prior Art
From the publication entitled“Dieselmotor-Management”, 2nd, Updated and Expanded Edition, Vieweg 1998, Braunschweig and Wiesbaden, ISBN 3-528-03873-X, page 270, FIG. 9, a pressure regulating valve used in a high-pressure pump is known; see page 267, FIG. 7, of the same publication. The pressure regulating valve includes a ball valve, which includes a spherical closing body. Received inside the pressure regulating valve is an armature, which on the one hand is acted upon by a compression spring and on the other has an electromagnet disposed opposite it. The armature of the pressure regulating valve is bathed with fuel for the sake of lubrication and cooling.
If the pressure regulating valve is not triggered, then the high pressure prevailing in the high-pressure reservoir or at the outlet of the high-pressure pump is present at the pressure regulating valve via the high-pressure inlet. Since the currentless electromagnet does not exert any force, the high-pressure force predominates over the spring force of the compression spring, so that the pressure regulating valve opens, and depending on the fuel quantity pumped remains more or less widely open.
Conversely, if the pressure regulating valve is triggered, that is, if current is supplied to the electromagnet, then the pressure in the high-pressure circuit is increased. To that end, a magnetic force is generated, in addition to the force exerted by the compression spring. The pressure regulating valve is closed until a force equilibrium prevails between the high-pressure force on the one hand and both the spring force and the magnet force on the other. The magnetic force of the electromagnet is proportional to the triggering current I of the magnet coils inside the pressure regulating valve. The triggering current I can be varied by means of clocking (pulse width modulation).
According to the aforementioned publication, page 270, FIG. 7, the pressure regulating valve is screwed into the high-pressure pump, for instance. The problem then arises that the requisite exact characteristic curve p=f(I), where I stands for the triggering current of the electromagnet, and where Q*=const., is dependent essentially on the air gap L that is established between the armature plate and the magnet core in which the magnet coils of the electromagnet are received. Upon mounting of the pressure regulating valve in a receiving body, in this case a high-pressure pump, for instance, the air gap L is adjusted. Depending on the air gap L, the characteristic curve of the pressure regulating valve, p=f(I), is established. The required tolerance in the aforementioned characteristic curve p=f(I) of the pressure regulating valve is adjusted at a test point, which is defined by a selected value for the triggering current I of the coils of the electromagnet. At this test point, a pressure tolerance of ±Δp of the pressure regulating valve is ascertained. The lower this tolerance proves to be, the better the attainable quality of regulation is in terms of the triggering behavior of the pressure regulating valve, and the more precisely the pressure regulating valve responds to pressure fluctuations between the high-pressure side and the low-pressure side.
Since the air gap L is dependent on the mounting quality and in the procedure of the prior art can be adjusted only at major effort, the pressure tolerance ±Δp established at the test point depends to a considerable degree on the quality of the mounting of the pressure regulating valve on a high-pressure pump, or on some other part subjected to high pressure.